1. Field of the Invention
The present invention relates to a seal structure for preventing powder or liquid contents of a casing from leaking from axial end portions of the casing, the casing containing a cylindrical member provided so as to be freely rotatable above and parallel to a bottom surface portion of the casing, and more particularly, to a seal structure that can be employed effectively with a development roller for a developing unit of an electronic photographic type image forming apparatus.
2. Description of the Related Art
A seal structure for preventing toner from leaking from the longer axial ends of a development roller that forms part of a developing unit in an electrophotographic image forming apparatus is disclosed in Japanese Laid-Open Patent Application No. 8-36306. FIG. 1 is a diagram showing a perspective view of a seal structure 51 provided at a front portion of a bottom part of a toner cartridge or casing 61 that also forms part of the developing unit 60, with FIG. 2 showing a frontal view thereof. It should be noted that although FIGS. 1 and 2 show only the left half of the developing unit 60, the right half has an identical corresponding structure.
To proceed with a description of the seal structure 51, the front portion of the bottom part of the toner casing 61 is openly disposed opposite a photosensitive drum not shown in the diagram, with a developing roller 52 provided at the open part. A toner supply roller not shown in the diagram is provided at the back of the developing roller 52 and in contact with the developing roller 52. The photosensitive drum would be positioned at the front of the developing roller 52 shown in FIG. 2, that is, between the observer and the sheet of paper on which the diagram is printed.
In the development process according to the developing unit 60, the toner inside the toner casing 61 is supplied to the photosensitive drum via the toner supply roller and the developing roller 52. In this case, a rotation of the developing roller 52 in a direction indicated by the arrow B in FIGS. 1 and 2 supplies the toner at the bottom portion of the interior of the toner casing 61 to the photosensitive drum, with any toner that did not contribute to the development of the image being scraped from the drum by a recovery blade not shown in the diagram and returned to the interior of the toner casing 61.
The seal structure 51 described above prevents toner T remaining in the space between the bottom of the developing roller 52 and the floor of the toner casing 62 from leaking into a space 55 on an outer side of an outer edge surface 52a of the developing roller 52.
According to the above-described seal structure 51, by using an adhesive and adhering a sheet-like seal member 53 to a toner casing floor portion 63 disposed opposite a lower outer edge of the developing roller 52, the lower outer edge of the developing roller 52 and the corresponding floor portion 63 compressively deform the seal member 53. In other words, the floor portion 63 becomes an adhesive surface for the seal member 53. However, in the course of the developing process the outer edge of the developing roller 52 is compressed as it rotates by the seal member 53, unavoidably generating a certain amount of heat.
In the above-described seal structure 51, the outer edge of the developing roller 52 is parallel to the casing floor 62 and the seal member 53 is of uniform thickness as it is adhered to the adhesive surface 63, so the seal function is effected by uniformly compressively deforming the seal member 53. Such an arrangement poses a number of disadvantages. For example, if the seal pressure is low (that is, if the amount by which the seal member 53 is deformed is small), then the toner T can leak out into the space 55 via the contact between the outer edge of the developing roller 52 and the seal member 53. Additionally, if the seal pressure is increased to counteract the above-described possibility and to more securely prevent leakage of the toner, then there is the disadvantage of an increase in the amount of frictional heat generated at the point at which the outer edge of the developing roller 52 and the seal member 53 contact each other. In extreme cases, the toner itself is melted by the heat so generated. Although to some extent it is possible to reduce the amount of heat generated by friction by making the surface of the seal member smoother and more slippery so as to reduce friction, there is a limit to what such countermeasures can achieve.
It is a general object of the present invention to provide an improved and useful seal structure in which the above-described disadvantages are eliminated.
A more specific object of the present invention is to provide an improved and useful seal structure in which the contents of the casing (whether in powder or liquid form) are prevented from leaking outside thereof.
Another and more specific object of the present invention is to provide an improved and useful seal structure in which a rise in temperature due to heat caused by friction between the cylindrical member and the seal member can be reduced.
The above-described objects of the present invention are achieved by a seal structure comprising a seal member for preventing toner from leaking out of a casing, the seal member adhesively provided and compressively deformed between an interior floor portion of the casing and a lower outer edge portion of a cylindrical member disposed so as to rotate freely above and parallel to the interior floor of the casing, the seal member being made of an elastic material and disposed so that a degree of compressive deformation of the seal member is greater toward a longitudinal center of the cylindrical body in an axial direction thereof than at the outer edge of the cylindrical body.
According to the above-described aspect of the invention, the sealing function of the seal structure is greatly improved over the conventional art and leakage of the toner from the axial ends of the casing can be securely prevented. Additionally, the amount of heated generated by friction between the seal member and the static parts of the unit is reduced, thus preventing the toner from melting.
The above-described objects of the present invention are also achieved by the seal structure as described above, wherein the seal member is a sheet of uniform thickness and a portion of the interior floor of the casing to which the seal member is adhered is higher toward the longitudinal center of the cylindrical member than toward the edge of the cylindrical member.
According to the above-described aspect of the invention, the seal structure can be produced simply and inexpensively because the seal member can continue to be made of a single strip of uniform thickness while the slant of the adhesive surface allows differential pressure to be applied to different part of the seal member so as to provide a better seal.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.